1. Field of the Invention
The present invention relates to a data transfer system and a data transfer method, in which a C-plane controller and a U-plane controller are separated from each other and the C-plane controller selects an optimum transmission line.
2. Description of the Prior Art
AUTRAN (Universal Terrestrial Radio Access Network) is a node which is positioned between a UE (User Equipment) or a user terminal such as a mobile phone or the like and a CN (Core Network) such as a switched network or the like and realizes an interconnection of their interfaces. An RNC (Radio Network Controller) accommodates a plurality of radio base stations via Iub interfaces for connecting the radio base stations to the RNC and carries out a variety of processing relating to control channels (CCHs) for communicating control information or data and traffic channels (TCHs) for transmitting user data. In this case, a common channel is commonly shared among users and an individual channel is assigned to each user.
In recent years, there has been spirited debate about all IP networking of the RNC as a controller of radio base stations in standardization of 3GPP (3rd Generation Partnership Projects). Since an increase of a using rate of a U-plane (user data plane) is expected in the future, it is necessary to consider the RNC in which a C-plane (control plane) and the U-plane are separated from each other. A new problem arises in the RNC realizing the all IP networking and the C-plane/U-plane separation. That it, the RNC is required not only to ensure operations realized in conventional systems but to control a plurality of U-plane controllers by one C-plane controller, which is considered in the C-plane/U-plane separation condition. For this new problem, an effective resource using system has not been made clear in the standardization of the 3GPP.
As mentioned above, the C-plane represents the control plane, that is, a link through which control message data passes between devices, and the U-plane the user data plane, that is, a link through which various contents data actually passes between the users.
Conventionally, a function for controlling a C-plane and a U-plane has been realized within one device and the links where the data has flowed have passed through the same route. The controllers for the C-plane and the U-plane are separated from each other in order to realize a network structure to meet various scalabilities. This concept is called separation of planes or the C-plane/U-plane separation.
Another technique has been proposed, as disclosed in Japanese Patent Laid-Open Publication No. 2004-48209. That is, when a U-plane controller for user data is congested in a wide band-code division multiple access communication system, a part of its processing is treated by another backup U-plane controller to maintain the processing. As a result, when an increase of the user data is expected, the processing of the user data within a network can be readily distributed to prevent the whole system from going down.
However, in this conventional system, problems still arise. That is, the radio base stations are necessarily in a one-to-one correspondence with the U-plane controllers, and if the load of the processing in a layer of the U-plane controllers can be distributed, one for realizing an optimum transmission line cannot be selected from a plurality of U-plane controllers depending on either an increase or a decrease of user data traffic within a service area.